This invention relates to the design and use of a unique disc prosthesis for the lumbar and thoracic spine. By placing one or more ovoid resilient prosthetic nuclei in series inside a peanut-shaped housing of metal ceramic or polymeric material, which housing is shaped so that it is separated into two sections longitudinally, a thin profile prosthesis can be created which will allow placement of the device through a small opening for implant into the thoracic or lumbar portion of the spine.
U.S. Pat. No. 5,674,296 is incorporated by reference.
Degenerative disc disease, including disc herniation, may produce disabling symptoms of local pain, radiculopathy or myelopathy in an otherwise clinically stable spine, and may be unresponsive to non-surgical treatment. Several surgical treatments are available to address the symptoms of degenerative disc disease when non-invasive therapies are not effective. These surgical treatments include decompression, discectomy and fusion. These treatments, and in particular the discectomy and fusion procedures, provide relief of clinical symptoms but they do not restore normal or near normal range of motion or cushioning to the affected functional spinal unit (FSU). This can result in acceleration of the degenerative process in spinal discs adjacent to the original surgical operation site. This degenerative process can, in turn, require additional surgical intervention.
Open surgery and endoscopic techniques are often used to provide access to the targeted intervertebral disc space. Posterior, postero-lateral, and anterior approaches allow placement of instrumentation to facilitate exposure of the degenerated disc and the insertion of bone grafts or fusion cages to accomplish bony fusion.
Because of anatomical structure considerations and instrument size restrictions associated with minimally invasive surgical techniques in the anterior lumbar spine, the insertion of a functional disc prosthesis equal in size to the natural disc creates risks due to mechanical interferences with critical vascular structures.
A functional disc prosthesis which provides for a full range of motion of the FSU and for cushioning between two adjacent vertebrae while maintaining stability, intervertebral body spacing and lordosis, is desirable.
More specifically it is an object of the invention to provide a disc prosthesis having a small or narrow profile. The novel exemplary prosthesis has an exterior shape like that of a peanut shell. This peanut shaped housing is comprised of two longitudinally split halves. Each housing half is separated from the other at all times by disk shaped resilient bodies contained therein, and is strong enough to support the loads to which it shall be subjected during the activities of daily living. The discoid nuclei are of smaller diameter than the natural discs they replace, and are positioned in the shell concave interiors of the peanut shaped housing. The housing is configured to accommodate the restrictions imposed by the limited anatomical space available for the surgical placement of the implant, and is small so as to utilize implantation procedures and instrumentation such as those used in an endoscopic procedure.
It is a further object of the invention to provide geometry to engage concave mating surfaces on the vertebral bodies or bones so as to provide proper stability and proper positioning of the opposing engaged vertebrae or vertebral bodies.
Another object is to obviate the need for a second surgical site for bone graft harvesting as may be required when spinal fusion cages are implanted.
And it is a further object of the invention to provide a sheath so as to completely surrounded and enclose the space occupied by the resilient bodies between the two housing halves, thereby restricting the migration of debris outside the prosthesis, restricting cancellous tissue ingrowth into the device, and providing a sealed space around the prosthetic nucleus in which lubricant may be contained.
Still another object of the invention is to provide a disc prosthesis which will permit motion between the housing halves.
A further object of the intention is to provide a disc prosthesis which will provide for cushioning between the housing halves.
It is a still further object of the invention to provide a disc prosthesis which may be used alone or in parallel array with similar prostheses.
It is yet another object to provide a housing having one or more ports through which a liquid (for example, a saline fluid, hyaluronic acid, or similar lubricating fluid material including for example a hydrogel material) can be introduced into the housing interior space confined within the sheath and partly occupied by the disc for purposes of lubrication, spacing, and/or cushioning. A plug, screw or other can also be provided to seal closed the port following introduction of that material.
Other objects and advantages of the invention will become apparent to those skilled in the art upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.